There are several basic single or combination topologies commonly used to implement switching converters.
One of the topologies is the push-pull converter. The output signal is derived from the output of an IC network that switches the transistors alternately “on” and “off”.
High frequency square waves on the transistor output drive the magnetic element into AC (alternating current) bias. The isolated secondary outputs a wave that is rectified to produce DC (direct current). Push-pull converters generally have more components as compared to other topologies. The push-pull approach makes efficient use of the magnetic element by producing AC bias, but suffers from high parts count, thermal derating, oversized magnetics, and elaborate core reset schemes.
The destructive fly-back voltages occurring across the switches are controlled through the use of dissipative snubber networks positioned across the primary switches. Another of the topologies is the forward converter. When the primary of the forward converter is energized, energy is immediately transferred to the secondary winding. In addition to the aforementioned issues the forward converter suffers from inefficient (dc bias) use of the magnetic element. The prior art power supplies generally use high permeability gapped ferrite magnetic elements. These are well known in the art and are widely used. The magnetics of the prior art power supplies are generally designed for twice the required power rating and require complex methods to reset and cool the magnetic elements resulting in increased installed costs, size, complexity and limited operating temperatures. This is because high permeability magnetic elements saturate during operation producing heat in the core, which increases permeability and lowers the saturation threshold. This produces runaway heating, current spikes and/or large leakage currents in the air gap, reduced efficiency, and ultimately less power at higher temperatures and/or high load. The overall effects are, lower efficiency, lower power density, and forced air/heatsink dependant supplies that require over-rated ferrite magnetic elements for a given output over time, temperature, and loading.